We can survive for weeks without food, but only days without water: it is the essential element of life. Yet many millions of us live in parched deserts around the world. In the second episode of Human Planet, we discover how the eternal quest for water brings huge challenges - and ingenious solutions - in the driest places on Earth. Battling through a sand storm in Mali, Mamadou must get his cows to a remote lake but desert elephants have arrived first. Can he find a safe way through the elephant blockade? Alone for weeks on end, Tubu women and children navigate the endless dunes of the Sahara. How does young Shede know where to find the last oasis, three days walk across the sea of sand? At the height of the drought we witness a spectacular frenzy: two thousand men rushing into Antogo Lake to catch the fish trapped by the evaporating water. When the rain finally arrives in the desert it's a time for flowering and jubilation - and love. The Wodaabe men of Niger put on make-up for an intoxicating courtship dance and beauty contest.

The Arctic is the harshest environment on Earth: little food grows, it's dark for months on end, and temperatures stay well below freezing for much of the year. Yet four million people manage to survive here. Human Planet tells remarkable stories of extraordinary people who make their homes in nature's deep freeze. In springtime, Amos and Karl-Frederik set out across the sea ice with their dogs to catch a real-life sea monster: a Greenland shark! Inuit mussel-gatherers venture underneath the sea ice at low tide for a perilous race against time as they gather their food. And the children of Churchill, Manitoba, set out on the most dangerous trick or treating Halloween in the world: they risk coming face-to-face with deadly polar bears on the streets of their town. Who'll get the tastiest snack?

Grasslands feed the world. Over thousands of years, we humans have learned to grow grains on the grasslands and domesticate the creatures that live there. Our success has propelled our population to almost seven billion people. But this episode reveals that, even today, life in the 'Garden of Eden' isn't always rosy. We walk with the Dorobo people of Kenya as they bravely attempt to scare off a pride of hungry lions from their freshly caught kill. We gallop across the Steppe with extraordinary Mongolian horsemen who were 'born in the saddle'. And in a perfect partnership with nature built up over generations Maasai children must literally talk to the birds! The honeyguide leads them to find sweet treats, but they'll have to repay the favour.

Are the wealthy just born in the right place at the right time? Are the poor victims of a system designed to keep them down? Or do physics and biology determine who is rich and who is poor? Throughout history, distribution of wealth is governed by hidden forces: DNA, environmental stress, patterns of human migration and even the laws of thermodynamics! Nature seems to demand winners and losers in life. But does this mean greed is king, and the rich can take what they want? Or is cooperation – between microorganisms, monkeys, and humans – more essential to survival of a species?

Researchers discuss the possibility that the creation of the Large Hadron Collider was foretold in ancient sources that were inspired by aliens

We live our lives pursuing happiness 'out there' as if it is a commodity. We have become slaves to our own desires and craving. Happiness isn't something that can be pursued or purchased like a cheap suit. This is Maya, illusion, the endless play of form. In the Buddhist tradition, Samsara, or the endless cycle of suffering is perpetuated by the craving of pleasure and aversion to pain. Freud referred to this as the "pleasure principle." Everything we do is an attempt to create pleasure, to gain something that we want, or to push away something that is undesirable that we don't want. Even a simple organism like the paramecium does this. It is called response to stimulus. Unlike a paramecium, humans have more choice. We are free to think, and that is the heart of the problem. It is the thinking about what we want that has gotten out of control. The dilemma of modern society is that we seek to understand the world, not in terms of archaic inner consciousness, but by quantifying and qualifying what we perceive to be the external world by using scientific means and thought. Thinking has only led to more thinking and more questions. We seek to know the innermost forces which create the world and guide its course. But we conceive of this essence as outside of ourselves, not as a living thing, intrinsic to our own nature. It was the famous psychiatrist Carl Jung who said, "one who looks outside dreams, one who looks inside awakes." It is not wrong to desire to be awake, to be happy. What is wrong is to look for happiness outside when it can only be found inside.